Minimum shift keyed (MSK) modulation has received considerable attention over the past decade due to its potential as a bandwidth and power efficient constant envelope modulation technique. Two generic techniques for the modulation and demodulation of MSK signals are referred to as the parallel and serial methods. Both are completely equivalent in terms of bandwidth occupancy and bit error rate (BER) performance.
With the series approach, the MSK modulated signal is produced from a bi-phase modulated signal by filtering it with an appropriately designed conversion filter. This method is described in detail in a copending application entitled "Serial Minimum Shift Keyed Modulator", assigned to the same assignee and filed of even date herewith. Since the advent of serial minimum shift keyed (SMSK) modulation, the general trend has been to construct single channel demodulators which operate essentially in the reverse of the SMSK modulators. See, for example, F. Amoroso and J. A. Kivett, "Simplified MSK signaling Technique", IEEE Transactions on Communications, Volume Com-25, pp. 433-441, April 1977. All of the single channel SMSK demodulators require a matched filter which is relatively difficult to construct and there is no indication if the output is locked or coherent.